Composition for film formation, laminate, film, sheet base material, method for producing a composition for film formation, and method for preparing a cellulose dispersion

ABSTRACT

A method for preparing a cellulose dispersion includes oxidizing cellulose; preparing cellulose nanofibers by defibrating the oxidized cellulose; and adding a water-soluble polymer and inorganic particles to the dispersion containing the cellulose nanofibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority benefit to U.S.patent application Ser. No. 14/222,212, filed Mar. 21, 2014 and issuedas U.S. Pat. No. 9,481,805, which is a continuation of and claims thebenefit of International Patent Application No. PCT/JP2012/073813, filedSep. 18, 2012, and claims the foreign priority benefit of JapanesePatent Application No. 2011-207969, filed Sep. 22, 2011, and JapanesePatent Application No. 2011-215176, filed Sep. 29, 2011, the disclosuresof which are incorporated herein by reference.

This invention relates to a composition for film formation, a laminate,a film, a sheet base material and a packaging material, which areproduced by effective use of cellulose materials as a natural source,and also to a method for preparing a composition for film formation anda method for preparing a cellulose dispersion. The invention relatesfurther to a gas barrier laminate formed by using the cellulosedispersion and a packaging material obtained by use of the gas barrierlaminate.

In the field of packaging materials for foods and medicines, it isnecessary for packaging materials to have barrier properties so as toprotect contents by shielding against gases, such as oxygen, water vaporand the like, passing through the packaging material, and also toprotect them from flavors and smells from inside and outside thepackaging material and low molecular weight substances contained infilms and adhesives, and also from light, etc.

There have been hitherto used, as the barrier material, aluminum andpolyvinylidene chloride that are less susceptible to temperature andhumidity. With aluminum, however, a problem is involved in that whenaluminum is incinerated, the resulting incineration residue may beclogged in an exhaust port and the inside of an incinerator therebylowering an incineration efficiency. With the incineration ofpolyvinylidene chloride, there arises a problem such as of occurrence ofdioxins. Hence, there have been demanded substitutes with materialswhich are reduced in load on the environment.

With regard to substitute materials of aluminum and polyvinylidenechloride, as described, for example, in Patent Literature 1, partialsubstitution with aluminum or chlorine-free polyvinyl alcohol orethylene/vinyl alcohol copolymers has been in progress although thesematerials are made of similar fossil resources. In this regard, futurechanges are expected to replace petroleum-derived materials by biomassmaterials.

Until now, attention has been paid to cellulosic materials as a newbarrier material. Cellulose occupies approximately a half of biomassmaterials produced on the earth. Since cellulose is not onlybiodegradable, but also excellent in physical characteristics such asstrength, elastic modulus, dimensional stability, heat resistance,crystallinity and the like, the applications thereof to functionalmaterials have been expected. As is particularly set forth in PatentLiteratures 2 and 3, it is known that cellulose nanofibers, obtained bydispersing oxidized cellulose obtained by oxidation reaction by use of2,2,6,6-tetramethyl-1-piperidine-N-oxy radical catalyst (hereinafterreferred to as TEMPO), are able to form a film. This film has, asidefrom the properties inherent to cellulosic materials, excellenttransparency and barrier properties under dried conditions. In PatentLiterature 4, there is described a barrier film including amoistureproof layer in addition to a cellulose nanofiber layer.

However, the film made of cellulose nanofibers has problem in thatproperties, such as barrier properties, lower owing to its moistureabsorption and swelling under high humidity conditions. With the barrierfilms described in Patent Literature 4 and provided with themoistureproof layer along with the cellulose nanofiber layer, themoisture absorption and swelling of the cellulose nanofibers aresignificantly influenced, so that the above problem cannot be solved.Thus, there has been demanded a method of imparting a moistureresistance to the cellulose nanofibers per se so as to prevent themoisture absorption and swelling of the cellulose nanofibers.

Cellulose fibers are able to form a film which is excellent in strengthand flexibility because of the structure where fibers are mutually,densely entangled. In this regard, however, such a structure has anumber of interstices, which permit deterioration factors such as ofwater vapor, contaminants in air and the like to be readily infiltratedand permeated thereinto, thereby inviting the degradation of the filmand an underlying base material. Especially, the infiltration of watervapor is undesirable because it serves to cause the lowering ofperformance of cellulose having high moisture absorption.

In order to improve the barrier properties of cellulose at highhumidity, it is considered that a layered inorganic compound, such asmica or montmorillonite, is blended with cellulose fibers. Where abarrier layer is formed of a composition for film formation where alayered inorganic compound is mixed with cellulose fibers, the barrierproperties are remarkably improved due to the tortuosity effect of thelayered inorganic compound. In this regard, however, in order that highbarrier properties are shown, it is necessary to increase an amount oflayered inorganic compound. Nevertheless, if the amount of a layeredinorganic compound exceeds a given level, a problem is involved in thatthe film strength (film cohesion) lowers considerably.

Where a barrier layer having low film strength is used as a packagingmaterial, peeling strength sufficient for the packaging material cannotbe obtained because of the weak strength of the barrier layer itselfregardless of how firm its adhesion with a base material or sealantlayer is.

Under these circumstances, as described in Patent Literature 5, therehas been proposed a material comprising cellulose fibers, a layeredinorganic compound, and a barrier material containing a water-solublepolymer. This enables the water-soluble polymer to be filled between thecellulose fibers and the layered inorganic compound thereby ensuringimproved film strength of the barrier layer per se.

PRIOR-ART LITERATURE Patent Literature

Patent Literature 1: Japanese Patent Application Publication No.H07-164591

Patent Literature 2: Japanese Patent Application Publication No.2008-30882

Patent Literature 3: Japanese Patent Application Publication No.2008-1728

Patent Literature 4: Japanese Patent Application Publication No.2009-57552

Patent Literature 5: Japanese Patent Application Publication No.2012-149114

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

With the barrier material set forth in Patent Literature 5, however, notonly its strength has not been sufficient to withstand use as actualpackaging material, but also an improvement in barrier properties,particularly, an remarkable improvement thereof at high humidity, couldnot be found.

The invention has been made in view of those set out above and has forits object the provision of a composition for film formation comprisingcellulose fibers, an layered inorganic compound and a water-solublepolymer, which are, respectively, dispersed at nano levels, a method forproducing such a composition for film formation, and a film formed ofthe composition for film formation. The invention also has as its objectthe provision of a sheet base material and a laminate, which are capableof further improving the barrier properties of cellulose film at highhumidity and suppressing the infiltration and permeation, into the film,of water vapor and contaminants serving as deterioration factors.Additionally, the invention provides for its object the provision of apackaging material having film strength sufficient to withstand usealthough a layered inorganic compound is contained.

Further, because of the problem that a film containing cellulosenanofibers lowers in properties such as gas barrier properties due tothe moisture absorption and swelling of the cellulose under highhumidity conditions, there has been demanded a method for impartingcellulose nanofibers per se to moisture resistance.

To this end, the invention has been made to overcome the above problemand has for its object the provision of a method for preparing acellulose dispersion capable of preparing a film containingmoistureproof cellulose nanofibers.

Means for Solving the Above Problems

As means for solving the afore-stated problems, (1) a composition forfilm formation according to one embodiment of the present invention ischaracterized in that the composition for film formation contains atleast cellulose fibers and a swollen layered inorganic compound.

It is preferred that an average particle size of the swollen layeredinorganic compound is within a range of from 0.5 μm to 10 μm, morepreferably from 3 μm to 7 μm.

It is also preferred that the average particle size of the swollenlayered inorganic compound is from 1.01 to 5.00 times the size prior toswelling.

It is preferred that from 20 wt % to 100 wt % of water is contained in asolvent.

Preferably, a water-soluble polymer is further contained.

Further, it is preferred that the composition contains at leastcellulose fibers and a swollen layered inorganic compound wherein itstotal light transmittance after dilution to 1% is within a range of fromnot less than 20% to not larger than 80%, more preferably from not lessthan 40% to not larger than 80%.

(2) A laminate according to another embodiment of the invention ischaracterized in that the composition for film formation of (1) above isdried and stacked on at least one surface of a base material.

Preferably, the haze value is at 5% or below.

It is preferred that a fracture strength of the film is not less than 1N/15 mm in a direction perpendicular to the surface direction of thelaminate.

(3) A film according to a further embodiment of the invention ischaracterized in that the composition for film formation as recited in(1) above is dried.

It is preferred that individual gaps between the layers of the layeredinorganic compound are not less than 14 angstroms.

If the film has a thickness of 0.1-30 μm, the total light transmittancethereof is not less than 90% at a wavelength of 600 nm.

Further, it is characterized that the layered inorganic compound has athickness of not less than 10 nm in a direction perpendicular to thesurface direction of the film.

(4) A sheet base material according to a further embodiment of theinvention is characterized in that the sheet base material is made ofthe film according to any one of (1) to (3) above.

(5) A packaging material according to a still further embodiment of theinvention is characterized in that the packaging material makes use ofthe film as recited in any one of (1) to (3) above.

A packaging material according to another embodiment of the invention ischaracterized in that the packaging material is made of the film of (4)above.

A method for producing a composition for film formation according toanother embodiment of the invention is characterized by comprising thestep of mixing a dispersion of a swollen layered inorganic compoundhaving an average particle size within a range of from not less than 0.5μm to not larger than 7 μm and a dispersion of cellulose fibers havingan average particle size of not larger than 300 nm.

Another embodiment of the invention made to solve the foregoing problemsis directed to a method of preparing a dispersion of cellulose ischaracterized by comprising the steps of oxidizing cellulose,defibrating the oxidized cellulose to prepare cellulose nanofibers, andadding a water soluble polymer and inorganic particles to a dispersioncontaining the cellulose nanofibers.

In another embodiment of the invention, the step of adding thewater-soluble polymer and the inorganic particles may be carried out bymixing an aqueous solution of the water-soluble polymer with theinorganic particles and subsequently agitated, followed by addition tothe dispersion containing the cellulose nanofibers.

Further, in another embodiment of the invention, the step of adding thewater-soluble polymer and inorganic particles may further include theheating step after mixing and agitation of an aqueous solution of thewater-soluble polymer and the inorganic particles.

In still another embodiment of the invention, the step of adding thewater-soluble polymer and inorganic particles may further include thesteps of preparing a mixed dispersion of the water-soluble polymer andinorganic particles and subsequently adding to a dispersion containingthe cellulose nanofibers, and heating the thus added dispersion.

In another embodiment of the invention, the step of adding thewater-soluble polymer and inorganic particles may be carried out byadding the inorganic particles to a dispersion containing cellulosenanofibers and agitating, followed by addition of the water-solublepolymer thereto.

In a further embodiment of the invention, the step of adding thewater-soluble polymer and inorganic particles may include, afteraddition of the inorganic particles to a dispersion containing thecellulose nanofibers and agitation, the step of heating the thusagitated dispersion.

In another embodiment of the invention, the step of adding thewater-soluble polymer and inorganic particles may include, afterpreparation of a mixed dispersion of the cellulose nanofibers and theinorganic particles, the steps of adding the water-soluble polymer tothe mixed dispersion and heating the thus added mixed dispersion.

A yet further embodiment of the invention is directed to a gas barrierlaminate, characterized by coating the cellulose dispersion preparedaccording to the method of preparing a cellulose dispersion of the aboveembodiment onto at least one surface of a base material.

Yet another embodiment of the invention is directed to a packagingmaterial, characterized in that a heat-sealable thermoplastic resin isstacked on the gas barrier laminate of the above embodiment through anadhesive layer.

Effects of the Invention

The invention can provide a composition for film formation containingcellulose fibers, a layered inorganic compound and a water solublepolymer which are dispersed at nanometer level, respectively, a methodof producing the composition for film formation, and a film made of thecomposition for film formation. Further, there can be provided a sheetbase material and a laminate using the film, which are imparted withmoisture resistance and are further improved in barrier properties of acellulosic film at high humidity and which can suppress the infiltrationand permeation of deterioration factors, such as of water vapor,contaminants and the like, into the film. Moreover, there can beprovided a packaging material provided with film strength sufficient towithstand use although a layered organic compound is contained.

The invention can provide a coating dispersion (i.e. a cellulosedispersion) capable of forming a gas barrier layer that is lesssusceptible to environmental load by use of cellulosic materials.

Further, the addition of water-soluble polymer ensures improvedmiscibility between cellulose nanofibers and inorganic particles and isable to provide a coating dispersion capable of forming a composite filmwhich has high film strength and is improved in adhesion with a basematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows an example of a cross-sectional structure of a gasbarrier laminate according to an embodiment of the invention.

EMBODIMENT

An embodiment of the invention is now described.

The composition for film formation of this embodiment is characterizedby comprising cellulose fibers, a layered inorganic compound and awater-soluble polymer. Further, the invention is also characterized inthat the cellulose fibers, layered inorganic compound, and water solublepolymer are nano-dispersed.

The laminate of the embodiment is comprised of a base material and abarrier layer formed on at least one surface of the base material andcontaining at least the cellulose fibers and the water soluble polymer.

As the cellulose fibers contained in the barrier layer of theembodiment, there can be used those fibers having a fiber width within arange of between not less than 1 nm and not larger than 50 nm and afiber length of several μm. When the fiber width is within the aboverange, there can be obtained a transparent, high-strength film.Especially, it is preferred that the fiber width is within a range ofbetween not less than 1 nm and not larger than 10 nm, within which thecellulose fibers are more densely entangled, so that there can beobtained a film having excellent properties such as barrier propertiesand strength.

In the course of compositization with a layered inorganic compound,cellulose fibers are intercalated between the layers of the layeredinorganic compound when subjected to nano-dispersion. This makes itpossible to increase the moisture resistance and strength of the film.

The fiber width of cellulose fibers can be measured by dropping adroplet of an aqueous dispersion of 0.001 wt % of cellulose fibers ontoa mica substrate and drying to provide a sample. For the measurement ofthe fiber width, the surface profile is observed, for example, with AFM(Nano Scope, manufactured by Veeco Instruments Inc.), and a differencein height between the mica substrate and the fibers is regarded as thefiber width.

Whether the entanglement of fibers is dense or not can be judged, forexample, by surface observation using SEM (S-4800, manufactured byHitachi High Technologies Corporation) or by measurement of a specificgravity of cast film. As to the measurement of the specific gravity ofsuch a cast film, measurement can be made with a digital specificgravity meter (AND-DMA-220, manufactured by ANDO KEIKI CO., LTD.), andthe cast film provided as a sample can be prepared by pouring a givenamount of cellulose fiber aqueous dispersion into a rectangular casingmade of polystyrene and heating and drying the dispersion at 50° C. over24 hours.

According to the surface observation of the film containing cellulosefibers, the smaller number of interstices of the fibers and smaller sizethereof lead to a smaller fiber width, and according to the measurementof specific gravity, a higher specific gravity results in a smallerfiber width, thereby obtaining a film made of densely entangled fibers.Accordingly, further reduction in number of the interstices between thefibers can prevent the infiltration and permeation of deteriorationfactors such as of water vapor, contaminants and the like into the filmand thus, barrier properties of the barrier layer can be suppressed fromlowing at high humidity.

In this embodiment, there is used a water-soluble polymer that is wellcompatible with cellulose as a material capable of filling theinterstices existing inbetween the cellulose fibers in the film. Thecomposite film prepared by mixing cellulose fibers and a water-solublepolymer is able to suppress infiltration and permeation of deteriorationfactors such as of water vapor, contaminants and the like and eventuallyserves as a film showing excellent barrier properties in a high humidityenvironment.

For the water-soluble polymers, there can be used one or two or moreselected from synthetic polymers such as polyvinyl alcohol,ethylene-vinyl alcohol copolymer, polymethacrylic acid, polyacrylicacid, polyamine, polyurethane or derivatives thereof and water-solubleepoxy resins; and water-soluble polysaccharides such as polyuronic acid,starch, carboxymethyl starch, cationized starch, chitin, chitosan,carboxymethylcellulose, hydroxymethylcellulose, alginic acid, pectin,gelatin, guar gum, carrageenan, and derivatives thereof.

Among them, it is particularly preferred to select polyvinyl alcoholfrom the synthetic polymers. Polyvinyl alcohol having excellentfilm-forming properties, transparency, flexibility, etc., is wellcompatible with cellulose fibers, so that it is possible to readily fillthe interstices inbetween the cellulose fibers and form a film havingboth strength and flexibility. In general, polyvinyl alcohol (PVA) isone that is obtained by saponifying polyvinyl acetate. The term“saponification” used herein means to include from so-called partiallysaponified PVA in which several tens of percent of an acetic acid groupremains to fully saponified PVA in which only several percent of anacetic acid group is left.

Where polyvinyl alcohol is used as the water soluble polymer, it isespecially preferred that the ratio by weight ((A)/(B)) of cellulosefibers (A) and polyvinyl alcohol (B) is within a range of 50/50 to 95/5.With the case where partially saponified PVA selected among polyvinylalcohols is added, if the weight of the polyvinyl alcohol becomes largerthan the weight of the cellulose fibers outside this range, wettabilityagainst substrates made of plastic materials is improved. Nevertheless,a dispersion containing a coating agent unfavorably becomes one which issusceptible to foaming.

On the other hand, with the case where fully saponified PVA selectedamong polyvinyl alcohols is added, when the weight of polyvinyl alcoholbecomes larger than the weight of cellulose fibers outside the aboverange, the resulting dispersion becomes one which is less susceptible tofoaming. However, wettability against substrates made of plasticmaterials lowers thereby unfavorably causing a crawling failure or thelike.

With respect to the cellulose fibers according to this embodiment, acellulose fiber dispersion can be obtained by the following method.

First, the microfibril surfaces of cellulose are oxidized by acting anN-oxyl compound serving as an oxidation catalyst and an oxidizer on anatural cellulose starting material in water or water/alcohol. Next,after removal of impurities, dispersion treatment is carried out inwater or a mixed solution of water/alcohol to obtain a dispersion of thecellulose fibers.

For the starting natural cellulose, there can be used various types ofwood pulps obtained from softwood, hardwood, etc., nonwood pulpsobtained from kenaf, bagasse, straw, bamboo, cotton, seaweed, etc.,cellulose obtained from sea squirts, cellulose produced by microbes,etc. Further, it is difficult for various gases and molecules to enterthe inside of the cellulose crystals having many hydrogen bonds. Sincethe crystals are not loosened by the action of water (humidity), therecan be obtained a dispersion of cellulose fibers having a high degree ofcrystallinity. The degree of crystallinity ranges from 50% to 99%, andis preferably as high as not less than 70%. In particular, cellulose Iis preferred with respect to its crystal structure.

As the oxidation catalyst, a solution or suspension containing an N-oxylcompound, a co-oxidizer and an oxidizer is used. As the N-oxyl compound,there can be used TEMPO and derivatives thereof such as4-acetamide-TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO and the like.For the co-oxidizer, a bromide or iodine is preferred. Mention is made,for example, of an alkali metal bromide or alkali metal iodide. Inparticular, it is preferred to use sodium bromide having goodreactivity. Usable oxidizers include, a halogen, hypohalous acid orsalts thereof, halous acid or salts thereof, hydrogen peroxide, etc., ofwhich sodium hypochlorite is preferred.

In the reaction dispersion containing starting cellulose and anoxidation catalyst, the pH at which the oxidation reaction proceedsefficiently differs depending on the combination of chemicals used. Forexample, where TEMPO, and sodium hypochlorite and sodium bromide, bothserving as a co-catalyst, are contained, a preferred pH is within arange of not less than 9 to not larger than 12. Although it issufficient that the temperature conditions of the oxidation reaction arewithin a range of between not lower than 5° C. and not higher than 70°C., a temperature of not higher than 50° C. is preferred when taking itinto consideration that higher temperatures are more liable to causeside reactions.

With the oxidized cellulose, carboxyl groups are introduced onmicrofibril surfaces, and an osmotic pressure effect due to the mutualelectrostatic repulsion between the carboxyl groups allows themicrofibrils to readily become discrete (dispersed) on the order ofnanometers. In particular, in case where water is used as a dispersionmedium, the most stable dispersion state is given. In this regard,however, not only alcohols (such as ethanol, methanol, isopropanol,tert-butanol), but also ethers and ketones may be contained depending onthe drying conditions or various purposes such as of improvement andcontrol of liquid physical properties.

For the dispersion method of cellulose fibers, there can be used, forexample, any one or a combination of a mixer, a high-speed homomixer, ahigh-pressure homogenizer, a ultrasonic homogenizer, grinder grinding,freeze pulverization, a media mill, and a ball mill.

The barrier layer of this embodiment may contain a siloxane compound inaddition to the cellulose fibers and water soluble polymer. The siloxanecompound is one in which a hydrolyzate of a silane-coupling agent issubjected to siloxane bonding by condensation polymerization. Thecross-linked structure with the siloxane bonding has a significantlyhigh effect of suppressing swelling of the cellulose, in addition towater resistance and adhesion to a base material. In particular, thesiloxane compound obtained from tetraethyl orthosilicate has a highdegree of cross-linked structure formed only from the siloxane bonds, sothat infiltration of water vapor into the film can be most suppressed.

Other types of usable siloxane compounds include siloxane compoundsobtained from various silane coupling agents such as3-glycidoxypropyltrimethoxysilane, allyltriethoxysilane,3-aminopropyltriethoxysilane, and 3-propyltrimethoxysilane acrylate. Inthis embodiment, there may be used these siloxane compounds by mixingtwo or more thereof.

The barrier layer of the embodiment further contains a layered compound.For the layered compound, there can be used kaolinite, dickite,nakhlite, halloysite, antigorite, chrysotile, pyrophyllite,montmorillonite, beidellite, hectorite, saponite, stevensite,tetrasilicic mica, sodium taeniolite, white mica, margarite, talc,vermiculite, brown mica, xanthophyllite, chlorite, etc. Commercialproducts include Sumecton SA (produced by Kunimine Industries Co., Ltd.)that has a saponite structure belonging to smectite based clay minerals,Kunipia-F (produced by Kunimine Industries Co., Ltd.) that is a sodiumtype of montmorillonite, and Bengel (produced by Hojun Co., Ltd.) thatis refined natural bentonite.

Further, various types of synthetic micas (produced by Topy Industries,Ltd., Co-op Chemical Co., Ltd.), etc., may be used as a syntheticlayered compound. In addition, layered compounds compositized withorganic compounds may also be used. For example, mention is made ofcomposite materials wherein quaternary ammonium ions having a long chainalkyl group are intercalated between layers through ion exchange.Commercially available products include Benton 27, Benton 38(manufactured by Elementis Specialties Inc.), etc. In particular, ifwater is contained in the solvent, it is not necessary to intercalate anorganic compound.

When a layered compound is contained in or inside a film, it isnecessary for various gases and molecules to bypass the layered compoundand pass through the film or sheet. Therefore, a layered compound havinga great aspect ratio should preferably be used so as to keep goodbarrier properties. It is preferred to use montmorillonite from theviewpoint of cost and to use synthetic mica from the standpoint ofbarrier properties.

Further, since a layered compound having a large aspect ratio results inlarge-sized aggregates, particles whose size is not smaller than 10 μmcan be confirmed through SEM or a microscope. When a non-dispersed andnon-swollen layered compound exceeds 7 μm in size, the surface roughnessdevelops and the resulting film becomes opaque along with theunlikelihood of improving barrier properties. The film becomes brittleand is weak in strength. Further, in a printing or bonding process forpostprocessing, an ink or adhesive is not attached uniformly, strengthbecomes uneven, and an outer appearance becomes worsened. It istherefore preferred to use a layered inorganic compound having anaverage particle size of from 0.5 μm to 7.0 μm in dry state. Morepreferably, there is used a layered inorganic compound having an averageparticle size of from 0.5 μm to 4.0 μm, much more preferably from 1.5 to3.5 μm.

If a layered inorganic compound in dried state has an average particlesize of larger than 7 μm, dispersion becomes difficult as illustratedhereinbefore, and barrier properties, strength and outer appearancebecome worsened. In case where aggregates are observed in rare cases dueto insufficient swelling treatment, a size of 4.0 μm or below leads togood dispersibility, and a size of 3.5 μm or below is more preferredbecause of high transparency. In contrast, when a dry particle size issmaller than 0.5 μm, good barrier properties cannot be shown.Especially, from the standpoint of barrier properties, a size of notsmaller than 1.5 μm is preferred.

This embodiment is further characterized by a composition for filmformation wherein an layered inorganic compound which has a relativelysmall average size in dried state is dispersed and swollen, under whichan average particle size in solvent is larger than the average size indried state. The average size in swollen state is preferably from notsmaller than 0.5 μm to not larger than 10 μm. If the average particlesize is smaller than this range, satisfactory barrier properties cannotbe shown. If the average particle size is larger than this range,aggregates appear and are unevenly distributed in a film or sheet. Whereswelling proceeds to a great extent, measurement with a particle sizeanalyzer reveals a smaller size owing to the scattered dispersion.

Further, the average particle size of a swollen layered compound in therange of from 3 μm to 7 μm is more preferred. This is becausetransparency becomes high and dispersibility is good, and good barrierproperties and high adhesion and strength are ensured. Especially, thosehaving a swollen average particle size of from 3.5 μm to 6 μm arepreferred: barrier properties become good, and dispersion and swellingproceed to optimal extents; and particularly, in a composite system witha water-soluble polymer, the water-soluble polymer is intercalatedbetween the layers of layered inorganic compound, so thatcompositization is likely to proceed upon mixing with cellulose fibers.

When observed through SEM, etc., or measured by means of a particle sizeanalyzer (e.g. SALD-2000 or SALD-7000 manufactured by SHIMADZUCORPORATION) after dispersion in a solvent such as, for example, water,etc., particularly without being subjected to swelling treatment,similar values are obtained with respect to the particle size in driedstate. For instance, one having an average particle size of 3.0 μm bySEM observation in dried state has an average size of 3.0 μm bymeasurement with an aqueous dispersion size analyzer. However, whenmeasured with a particle size analyzer after a layered compound as usedabove has been subjected to swelling treatment, the average particlesize is at 5.0 μm.

Further, a ratio by weight between cellulose fibers and layeredinorganic compound (weight of cellulose fibers/weight of layeredinorganic compound) contained in the composition for film formationaccording to the embodiment is preferably within a range of 99/1 to5/95. If the amount of layered inorganic compound is lower, satisfactorybarrier properties cannot be obtained, particularly, under high humidityconditions. When the amount of layered inorganic compound is too large,flaking of the layered inorganic compound becomes insufficient, therebyunfavorably lowering the barrier properties or resulting in a film whosestrength cannot be held and which is not flexible.

Further, the composition for film formation of the embodiment contains aswollen layered inorganic compound and is thus characterized in that itstotal light transmittance is from not less than 20% to not larger than90% when it is diluted to 1%. It is generally considered that whendispersibility is improved for the same amount of layered inorganiccompound, the total light transmittance is increased. However, withrespect to the composition for film formation of this embodiment, notonly dispersibility is improved, but also a layered inorganic compoundis swollen. In addition, a water-soluble polymer is intercalated betweenthe layers of cellulose fibers to provide an entangled, complicatedstructure, so that as both dispersability and their compositization areadvanced, the transmittance lowers. Thus, the film formed of thecomposition for film formation wherein the dispersibility and swellingor compositization of layered inorganic compound are advanced isimproved in barrier properties and film strength and has a low hazevalue.

Accordingly, if the transparency is higher than the above range and evenif dispersion is in progress, dispersibility is merely improved butswelling or compositization of the layered inorganic compound are notadvanced. The resulting film becomes unsatisfactory with respect to animprovement in barrier properties and film strength. On the other hand,the case where the transparency is smaller than this range isunfavorable. This is because there may be some cases where the resultingfilm is low in transparency, becomes high in haze and is unsatisfactoryin dispersibility.

Further, this embodiment is characterized in that a solvent is containedin the composition for film formation and water is contained in thesolvent at from 20 wt % to 100 wt %. The water content within this rangeis preferred because dispersibilities of a layered inorganic compound,water-soluble polymer and cellulose fibers are improved andcompositization is more advanced. Further, it is preferable to furthercontain an organic solvent for the purposes of improving a pot life anddispersion stability, etc., by suppressing foaming, increasing a dryingefficiency, preventing spoilage and the like. Examples of the organicsolvent include alcohols (ethanol, methanol, isopropanol, tert-butanol)and may include ethers, and ketones.

Further, additives may be added to the barrier layer in order to impartfunctionality. For example, it is possible to use, as an additive, aleveling agent, an antifoaming agent, a synthetic polymer, inorganicparticles, organic particles, a lubricant, an ultraviolet absorber, adye, a pigment, a stabilizer or the like. These additives may be addedto a coating dispersion within ranges not impairing barrier properties,and are also able to improve film characteristics depending on theintended use.

Next, a method for preparing the composition for film formationaccording to another embodiment is now described.

In this embodiment, cellulose fibers, layered inorganic compound andwater-soluble polymer are dispersed very well, and the cellulose fibersand water-soluble polymer are intercalated between the layers of thelayered inorganic compound thereby providing a very complicatedcomposite structure. Accordingly, the invention has the greatest featurein that the layered inorganic compound is swollen. To achieve this, thefollowing procedure is carried out.

Initially, a layered inorganic compound, prior to swelling, having anaverage article size of from 0.5 μm to 7 μm is swollen. A compositionfor film formation can be prepared by mixing a defibrillated cellulosedispersion and the layered inorganic compound.

As stated hereinbefore, the average particle size after swelling ispreferably at 0.5 μm to 10 μm, more preferably at 3 μm to 7 μm. Withinthis range, no limitation is placed particularly on the manner ofswelling. An instance of a swelling method is described below.

First, a layered inorganic compound is dispersed in water. At thisstage, swelling is hardly advanced. When the dispersion is subjected tovarious physical treatments, the layered inorganic compound can beswollen. For the physical treatments, mention is made, for example, ofany one of a stirrer, a mixer, a high-speed homomixer, a high-pressurehomogenizer, an ultrasonic homogenizer, grinder grinding, freezepulverization, a media mill, a ball mill, or a combination thereof.

The swelling can be more promoted by controlling physical treatingconditions such as time, the number of treatments, pressure,temperature, etc. In this regard, however, with respect to time, thenumber of treatments and pressure, if such treating conditions are settoo severely, the layered inorganic compound is broken and disrupted inthe in-plane thereof. The in-plane disruption leads to a lowering ofbarrier properties although dispersibility and swelling property areimproved. However, when the treating conditions is too mild, dispersionand swelling do not proceed. Accordingly, it is preferable to use, forphysical treatment, a mixer, a high-speed homomixer, a low-pressurehomogenizer, or an ultrasonic homogenizer. With regard to temperature,higher temperatures permit dispersion and swelling to more proceedunless the composition is changed as a result of vaporization,decomposition, etc., of the solvent used.

In order to promote swelling while suppressing the disruption to anextent as far as possible, there may be added surfactants, dispersants,inorganic salts, organic salts, organic compounds, etc., to variousdispersion aids.

The composition for film formation according to the embodiment ischaracterized by comprising a water-soluble polymer. When the watersoluble polymer is intercalated between the layers of a layeredinorganic compound, swelling is more promoted. Accordingly, it is mostpreferred to add a water-soluble polymer during the course of dispersionand swelling treatments of layered inorganic compound.

The water-soluble polymer is able to improve adhesion strength at theinterfaces between the cellulose fibers and the layered inorganiccompound. This mechanism is not known yet: when rigid cellulose fibersand a hard layered inorganic compound are mutually contacted with eachother, gaps are generated therebetween. When a water-soluble polymerhaving flexibility is entered into those gaps, adhesion strength at therespective interfaces can be improved.

Although no limitation is placed particularly on a ratio of the layeredinorganic compound and the water-soluble polymer, the water-solublepolymer can be added at a ratio by weight of from 0 to 5000, preferablyfrom 0 to 1000, relative to 100 of the layered inorganic compound. Whenthe amount of the water-soluble polymer is small, the dispersion andswelling of the layered inorganic compound becomes insufficient, withthe attendant problems that the resulting film having non-swollencompound is low in barrier properties and becomes opaque and thestability of dispersion becomes poor. On the other hand, when the amountof the water-soluble polymer exceeds the above range and thewater-soluble polymer is made of a synthetic polymer, the degree ofbiomass usage becomes small. Especially, under a high humiditycondition, some problems occur such that barrier properties lower and awater resistance lowers.

More preferably, the water-soluble polymer may be added at a ratio of100 to 500 relative to 100 of the layered inorganic compound. When theamount of the water-soluble polymer is within this range, thewater-soluble polymer is intercalated between individual layers of thelayered inorganic compound. At this time, because the amount of thewater-soluble polymer enables the layered inorganic compound to beswollen and its surplus amount is small, so that barrier properties canbe well shown.

The layered inorganic compound can be added to in the course of theafore-stated defibration treatment of cellulose fibers. The addition ofthe layered inorganic compound results in simultaneous treatmentsincluding the defibration treatment of cellulose fibers and theexfoliation treatment of the layered inorganic compound. For adispersion means, there can be used one or two or more selected from amixer treatment, a blender treatment, a ultrasonic homogenizertreatment, a high pressure homogenizer treatment, and a ball milltreatment. In this case, the water soluble polymer may be added eitherbefore or after the defibrating treatment.

When the above dispersion means is used, both the defibration of thecellulose fibers and the break-into-flakes treatment of the layeredinorganic compound can be performed simultaneously. Even if aqueousdispersions wherein cellulose fibers and a layered inorganic compoundare, respectively, dispersed are mixed, there may be some cases wherethe respective materials are not mixed uniformly and there cannot beobtained a film having excellent transparency, barrier properties andfilm strength as in this embodiment.

When using such a dispersion means as set out above, the layeredinorganic compound is broken into flakes and finely pulverized. Thistreatment enables coarse particles to be reduced into fine ones. Ifcoarse particles exist, coarse inorganic particles project from the filmsurface, with the possibility that an adhesive cannot be coateduniformly, resulting in the lowering of adhesion.

Further, there may be used a procedure of heating a dispersion of amixture of cellulose and layered inorganic compound or a mixture ofcellulose, water-soluble polymer and layered inorganic compound.

Using this technique makes it possible to exfoliate a layered inorganiccompound in the dispersion by application of heat energy. The heatingtemperature and time may be such that the time ranges from 40° C. to100° C. and the time ranges from 10 minutes to 20 hours. When taking itinto account that the layered compound is broken to lower barrierproperties, it is preferred that the temperature ranges from 40° C. to90° C. and time ranges from 10 minutes to 5 hours.

When a supersonic homogenizer or high-pressure homogenizer is used toexfoliate a layered inorganic compound, the layered inorganic compoundis broken into pieces and thus, barrier properties may become worsenedin some cases.

As previously stated, there may be used a technique of adding acellulose dispersion after mixing of a water-soluble polymer and alayered inorganic compound. When a layered inorganic compound havinghigh affinity for water-soluble polymer is used, it is possible toobtain a barrier film of better quality than in the case where celluloseis directly added. This is considered for the reason that where alayered inorganic compound and a water-soluble polymer are initiallymixed, the water-soluble polymer is intercalated between the layers ofthe layered inorganic compound more efficiently to expand the spacesbetween the respective layers thereby providing a film having a morecomplicated structure.

The dispersion obtained by mixing the water-soluble polymer and layeredinorganic compound may be heated. Upon heating of the dispersion, thelayered inorganic compound undergoes exfoliation, thereby ensuringbetter barrier properties. The heating temperature and time include from40° C. to 100° C. for the temperature and from 10 minutes to 20 hoursfor the heating time. When taking it into consideration that the layeredcompound is broken into pieces to lower barrier properties, atemperature of from 50° C. to 90° C. and a time of from 10 minutes to 5hours are preferred. In this regard, however, where this technique isadopted, a certain effect can be obtained when mere agitation over 10minutes to 20 hours is effected without heating. The above treatmentenables the surface area of the layered inorganic compound to bewidened, for which where the water-soluble polymer is not addedsufficiently, interstices of cellulose fibers and the layered inorganiccompound cannot be filled, with the possibility that film strength andadhesion become worsened.

In the present embodiment, the mixed dispersion is added to a cellulosedispersion. On this occasion, it is preferred to add the mixeddispersion of the layered inorganic compound and the water-solublepolymer while agitating the cellulose dispersion.

Subsequently, the mixed dispersion can be heated after the addition ofthe cellulose dispersion. This permits the layered inorganic compound tobe exfoliated in a similar way thereby improving barrier properties. Theheat temperature and time are from 40° C. to 100° C. for the temperatureand from 10 minutes to 20 hours for the heating time. However, when itis taken into account that the breakage of layered inorganic compoundinto pieces results in the lowering of barrier properties, a temperatureof 50° C. to 90° C. and a time of 10 minutes to 5 hours are preferred.

In the embodiment, cations present between the layers of the layeredinorganic compound may be substituted. When interlayer cations presentbetween the layers of the layered inorganic compound are contacted witha solution containing ions such as of ammonia, tetraethylammoniumhydroxide, tetrabutylammonium hydroxide, or the like, a substitutionreaction occurs instantaneously, so that cation exchange can becompleted. When the cation substitution is performed during the processof adding the layered inorganic compound, the layer-to-layer gaps of thelayered inorganic compound can be widened to obtain better barrierproperties.

The substitution of cations can be performed in a dispersion of layeredinorganic compound. Alternatively, it can be carried out either afteraddition to the cellulose dispersion or after addition to thewater-soluble polymer solution.

Besides, there may be used a procedure of adding to the system afterfreeze-pulverization of layered inorganic compound or after mortarpulverization subsequent to drying of layered inorganic compound. Theseprocedures enable the layered inorganic compound to be more finelypulverized and take a complicated structure, thereby leading to improvedbarrier properties.

In this way, the dispersed state of the materials contained in thebarrier layer-forming composition greatly influences the transparency,barrier properties, etc., when formed as a film. Especially, whendispersion is insufficient and non-uniform, film transparency andbarrier properties lower considerably. The barrier properties areimproved when the water-soluble polymer is intercalated between thelayers of the layered inorganic compound, and film strength is improvedby filling the gaps between the layered inorganic compound and thecellulose fibers with the water-soluble polymer. When the layeredinorganic compound is broken into fine pieces and dispersed, there canbe formed a film whose smoothness is kept and which is high is adhesion.

Additives may be further added to the coating dispersion according tothe embodiment of the invention so as to impart functionality. Forexample, it is possible to use a leveling agent, an antifoaming agent, asynthetic polymer, inorganic particles, organic particles, a lubricant,an ultraviolet absorber, a dye, a pigment, a stabilizer, etc. These canbe added to the coating dispersion within ranges not impairing gasbarrier properties, and may also improve film characteristics dependingon the intended use.

For a method of forming a gas barrier layer, known coating methods canbe used including, for example, those using a roll coater, a reverseroll coater, a photogravure coater, a micro-photogravure coater, a knifecoater, a bar coater, a wire bar coater, a die coater, a dip coater,etc. Using the above coating methods, at least one side of a substrateis coated. For a drying method, there can be used natural drying,air-blow drying, hot-air drying, UV drying, hot roll drying,infrared-ray irradiation, etc.

In order to improve film strength and adhesion, UV irradiation or EBirradiation treatment may be performed after formation of the gasbarrier layer.

Further, a gas barrier may be laminated thereon with an intermediatefilm layer, a heat-sealable thermoplastic resin layer (i.e. aheat-sealing layer), a printing layer, etc., if necessary, therebyproviding a packaging material. In addition, an adhesive layer (i.e. anadhesive layer for lamination) for lamination by a dry lamination methodor a wet lamination method, or a primer layer, an anchor coat layer,etc., in case where a heat-sealing layer is laminated using a meltingextrusion method may also be stacked.

Configuration examples (a)-(c) are shown, in which a gas barrierlaminate of the embodiment of the invention is used as a packagingmaterial. However, the gas barrier laminate according to the embodimentof the invention is not limited thereto.

(a) Base material 1/gas barrier layer 2/adhesive layer 4 forlamination/heat-sealing layer 6 (see FIGURE)

(b) Base material 1/gas barrier layer 2/printing layer/adhesive layer 4for lamination/heat-sealing layer 6

(c) Base material 1/gas barrier layer 2/adhesive layer 4 forlamination/intermediate film layer/adhesive layer 4 forlamination/heat-sealing layer 6.

The intermediate film layer is provided to enhance bag breakage strengthat the time of boiling and retort sterilization, and is usually selectedfrom a biaxially stretched nylon film, a biaxially stretchedpolyethylene terephthalate film, and a biaxially stretched polypropylenefilm from the viewpoints of machine strength and heat stability. Thethickness is determined depending on the type of material and requiredquality, etc., and is generally in the range of 10 μm to 30 μm. Thelamination is feasible by a dry lamination method wherein an adhesivesuch as a two-component urethane resin is used for lamination. In casewhere a base material 1 having gas permeability, such as paper, is used,lamination is possible by a wet lamination method using a starch-based,water-soluble adhesive, or an aqueous adhesive such as a vinyl acetateemulsion.

The heat-sealing layer 6 is provided as a sealing layer for forming abag-shaped packaging body, etc. For instance, there may be used a filmof a resin such as polyethylene, polypropylene, ethylene vinyl acetatecopolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylicacid ester copolymer, ethylene-acrylic acid copolymer, ethylene-acrylicacid ester copolymer, or a metal cross-linked product thereof. Althoughthe thickness of the heat sealing layer 6 is determined according to thepurpose, it is generally within a range of 15 μm to 200 μm. For aformation method, usual practice is to use a dry lamination method orthe like wherein a film serving as the heat sealing layer 6 is bonded byuse of an adhesive such as a two-component urethane resin. Anyway, thelamination can be effected by any of known methods.

As an adhesive used as the adhesive layer 4 for lamination, knownadhesives can be used depending on the types of materials of therespective layers to be laminated, including acryl-based,polyester-based, ethylene vinyl acetate-based, urethane-based, vinylchloride vinyl acetate-based, and chlorinated polypropylene-basedadhesives. For a coating method of an adhesive for forming the adhesivelayer 4 for lamination, known coating methods can be used, for whichthere are used, for example, a roll coater, a reverse roll coater, agravure coater, a micro-gravure coater, a knife coater, a bar coater, awire bar coater, a die coater, a dip coater, etc. The coating amount ofthe adhesive is preferably in the range of 1 g/m²-10 g/m².

The printing layer is formed for practical use as a packaging bag, andis one made of an ink in which various type of pigments, extenderpigments and additives, such as a plasticizer, a drying agent, astabilizer, etc., are added to ordinarily employed ink binder resins,such as urethane-based, acryl-based, cellulose nitrate-based,rubber-based and vinyl chloride-based resins. Characters, patterns,etc., are formed thereon.

The film and sheet of a further embodiment are now described. The filmand sheet of the embodiment can be formed by various types of coatings,castings, filterings, etc. More particularly, they can be prepared bycoating differently shaped base materials with the composition for filmformation of the embodiment according to various types of coatingmethods, followed by drying solvent. This will be explained hereinlaterwith regard to the illustration of laminate.

The base material may be replaced by a porous body, or the steps ofdehydration and filtration may be introduced prior to the drying. Thefilm and sheet can be made by adding a gelling agent or a poor solventto the film-forming composition to form a solid matter or gel, followingby filtration, dehydration and drying. The film and the sheet accordingto the embodiment contains a layered inorganic compound. An ordinarylayered inorganic compound has a layer-to-layer gap of approximately 12angstroms. For example, synthetic mica and montmorillonite prior toswelling has been found to have a layer-to-layer gap of 12 angstroms.The layer-to-layer gap can be measured by an X ray diffraction methodusing a bulk material obtained by drying the film-forming composition,the film or sheet formed. To read out from the diffraction peaks is themost accurate and simplest.

The film and sheet of the embodiment are characterized in that thelayer-to-layer gap of the layered inorganic compound determined by X-raydiffraction is not smaller than 14 angstroms. This demonstrates that thelayered inorganic compound is swollen, under which it forms a compositematerial along with cellulose fibers and a water-soluble polymer therebyforming the film or sheet. If the layer-to-layer gap is at 14 angstromsor over, compositization proceeds, with the result that the swelling ofthe cellulose fibers and water-soluble polymer under high humidityconditions can be suppressed. Because of the complexity of paths throughwhich various gases pass and the like, barrier properties are improved.Additionally, film permeability becomes high.

More preferably, the layered inorganic compound has a layer-to-layer gapof not less than 17 angstroms, under which compositization withcellulose fibers especially proceeds. This is considered for the reasonthat cellulose molecules at the sites of cellulose fibers where fluffedare considered to have a size of about 5 angstroms and are intercalatedbetween the respective interlayer gaps, thereby permitting thecompositization to proceed.

Next, the method for making a laminate of the embodiment is described.The laminate of the embodiment can be obtained by coating thefilm-forming composition of the embodiment onto at least one surface ofa base material and drying. For the base material, plastic materialsmade of a variety of polymer compositions can be used.

The plastic materials include, for example, polyolefins (polyethylene,polypropylene and the like), polyesters (polyethylene terephthalate,polyethylene naphthalate and the like), cellulose-based materials(triacetyl cellulose, diacetyl cellulose, cellophane and the like),polyamides (6-nylon, 6,6-nylon and the like), acrylic resins(polymethylmethacrylate and the like), polystyrene, polyvinyl chloride,polyimides, polyvinyl alcohol, polycarbonates, ethylene vinyl alcohol,etc. Additionally, there may be used organic polymer materials having atleast one component or copolymeric component, or a chemically modifiedcomponent thereof selected among those components of the above-indicatedplastic materials.

In recent years, there has been demanded the use of materials capable ofreducing an environmental load even if only slightly. To this end, theremay be used, as a base material of the embodiment, bioplasticschemically synthesized from plants, such as biopolyolefins, basematerials containing plastics produced by microorganisms, such ashydroxyalkanoates, or papers obtained through the pulping andpaper-making steps of woods, and plants and trees. Alternatively, theremay be used base materials containing cellulosic materials and includingcellophane, acetylated cellulose, cellulose derivatives and cellulosenanofibers.

In order to improve adhesion with the respective layers, the basematerial of the embodiment can be preliminarily subjected, on thesurfaces thereof, to surface modification such as by corona treatment,plasma treatment, frame treatment, ozone treatment, or anchor coatingtreatment.

As a base material of the embodiment, there may be used a base materialsubjected to vacuum deposition of ceramics. For the vacuum deposition ofceramics, there can be used, for example, those vacuum depositions ofaluminum oxide, magnesium oxide, tin oxide, silicon oxide and the like.Film-forming methods include a vacuum vapor deposition method, asputtering method, a plasma vapor phase epitaxial method, etc.

The shape of the base material is not particularly limited and can beappropriately selected from various types of moldings, such as a film, abottle, a cylinder and the like, although depending on the intended usethereof. Especially, when taking into consideration the transparency orflexibility of the cellulose fibers contained in the gas barrier layer,the base material is preferably in the form of a film and thus, aplastic film can be favorably employed. The film-shaped base materialmay be either stretched or non-stretched and should favorably have goodmechanical strength and dimensional stability. For instance, mention isfavorably made of biaxially, arbitrarily stretched polyethyleneterephthalate film and polyamide film. Moreover, the base material usedmay be one which is imparted with functionality by adding various typesof known additives and stabilizing agents such as, for example, aplasticizer, a lubricant, an antioxidant, an ultraviolet-ray inhibitorand the like.

It is possible to select the base materials appropriately depending onthe intended use. For example, in case where the laminate is used as apackaging material, a polyolefin-based, polyester-based, orpolyamide-based film is favorable from the viewpoints of price,mositureproofing, packageability, texture and disposability. For aneco-friendly material, paper, a polylactate film, and a polyurethane anda polyester that are synthesized from biomass raw materials,respectively, are more preferred.

For the film-forming method of the composition for film formation of theembodiment, know coating methods can be used including those using aroll coater, a reverse roll coater, a gravure coater, a micro gravurecoater, a knife coater, a bar coater, a wire bar coater, a die coater, adip coater, etc. Using the above coating methods indicated above, thecomposition for film formation is coated onto at least one surface of abase material. For drying, natural drying, air blow drying, hot airdrying, UV drying, hot roll drying, infrared-ray irradiation, etc., canbe used.

The film strength or adhesion may be improved by further subjecting toUV irradiation or EB irradiation treatment after the film formation.

The laminate of the embodiment is characterized in that its haze valueis not larger than 5%. This depends on the fact that cellulose fibersare fully fine on nano level and that a layered inorganic compound isfully dispersed. When the laminate has a haze value of not larger than5%, the use of the laminate as a packaging material is advantageous inthat the contents can be confirmed from outside.

If necessary, the film and sheet of the embodiment may be laminated withan intermediate film layer, a heat-sealable thermoplastic resin layer(heat-sealing layer), a printing layer, etc., for use as a packagingmaterial. In addition, an adhesive layer (adhesive layer for lamination)for laminating respective layers using a dry lamination method or a wetlamination method, or a primer layer, an anchor coat layer, etc., forlamination of a heat-sealing layer by a melt extrusion method may alsobe laminated. With impartment of better barrier properties, avacuum-deposition layer of a metal or metal oxide may be stacked.

Configuration examples (a)-(c) are shown, in which the laminate of thisembodiment is used as a packaging material. However, the laminate of theembodiment should not be construed as limited thereto.

(a) Base material/barrier layer/adhesive layer forlamination/heat-sealing layer

(b) Base material/barrier layer/printing layer/adhesive layer forlamination/heat-sealing layer

(c) Base material/barrier layer/adhesive layer forlamination/intermediate film layer/adhesive layer forlamination/heat-sealing layer.

The intermediate film layer is provided to enhance the bag breakagestrength during boiling and retort sterilization. In general, theintermediate film layer is selected, in most cases, from a biaxiallystretched nylon film, a biaxially stretched polyethylene terephthalatefilm, and a biaxially stretched polypropylene film from the viewpointsof machine strength and heat stability. The thickness is determinedaccording to the type of material, required quality, etc., and isgenerally within a range of 10 μm to 30 μm. For the formation, thislayer can be laminated by a dry lamination method using an adhesive,such as a two-component curable urethane resin or the like, for bonding.Where a base material having good gas permeability, such as paper, isused, lamination is feasible according to a wet lamination method usinga starch-based aqueous adhesive or an aqueous adhesive such as a vinylacetate emulsion.

The heat-sealing layer is provided as a sealing layer for forming abag-shaped package, etc. For example, there is used a film made of onekind of resin such as polyethylene, polypropylene, an ethylene vinylacetate copolymer, an ethylene-methacrylic acid copolymer, anethylene-methacrylic acid ester copolymer, an ethylene-acrylic acidcopolymer, an ethylene-acrylic acid ester copolymer, or a metalcrosslinked product thereof. Although the thickness of the heat sealinglayer is determined depending on the purpose, the thickness is generallywithin a range of 15 μm-200 μm. For the formation, usual practice is touse a dry lamination method of bonding the film by use of an adhesive,such as a two-component curable urethane resin. Nevertheless, any of thefilms can be laminated by known methods.

As an adhesive usable as the adhesive layer for lamination, knownadhesives including an acryl-based, polyester-based, ethylene vinylacetate-based, urethane-based, vinyl chloride-vinyl acetate-based andchlorinated polypropylene-based adhesives can be used although dependingon the types of materials of individual layers to be laminated. As acoating method of an adhesive for forming the adhesive layer forlamination, known coating methods can be used including, for example,those using a roll coater, a reverse roll coater, a gravure coater, amicro gravure coater, a knife coater, a bar coater, a wire bar coater, adie coater, a dip coater, etc. The coating amount of the adhesive ispreferably at 1-10 g/m².

The printed layer is formed in order to be practically used as apackaging bag or the like, and is one formed of an ink. The ink is madeof an ordinarily employed ink binder resin, such as a urethane, acryl,nitrocellulose, rubber, vinyl chloride or the like resin, to whichadditives such as various types of pigments, extender pigments,plasticizers, drying agents, stabilizers and the like, are added,thereby forming characters, designs, etc.

According to the embodiment stated above, there can be provided abarrier laminate which has a reduced burden on environment due to theuse of cellulose materials.

The method for preparing a cellulose dispersion (hereinafter referred tosimply as “coating dispersion”) according to still another embodiment ofthe invention is described in detail. The coating dispersion of theembodiment of the invention is made up of one that contains cellulosenanofibers (hereinafter referred to simply as “cellulose fibers”), awater-soluble polymer and a layered inorganic compound. It will be notedthat the term “inorganic particles used herein corresponds to “layeredinorganic compound” indicated in the foregoing embodiments.

Example 1

The embodiments of the invention are particularly described by way ofexamples. It is to be noted that the invention should not be construedas limited to these examples.

The respective materials of cellulose fibers, water-soluble polymers,layered compounds indicated below were mixed at formulation ratiosindicated in Table 1 to prepare coating dispersions.

TABLE 1 Example Example Example Example Example Example 1-1 1-2 1-3 1-41-5 1-6 Layered Kunipia Kunipia Kunipia Kunipia Synthetic Syntheticinorganic mica mica compound Average 0.5 0.5 0.5 0.5 3 3 particle sizeFormulation 1 1 1 1 1 1 ratio Water-soluble Polyvinyl PolyvinylWater-soluble Starch Polyvinyl Polyvinyl polymer alcohol alcoholpolyurethane alcohol alcohol Formulation 1 5 1 1 1 5 ratio Agitation 3080 30 80 80 80 temperature Water 98 94 98 94 98 94 Example Example Comp.Ex. Comp. Ex. Example Example 1-7 1-8 1-1 1-2 1-9 1-10 Layered SyntheticSynthetic Kunipia Synthetic Kunipia Synthetic inorganic mica mica micamica compound Average 6 3 0.5 3 0.5 3 particle size Formulation 1 1 1 11 1 ratio Water-soluble Polyvinyl Chitosan — — — — polymer alcoholFormulation 5 1 0 0 0 0 ratio Agitation 80 30 30 30 80 80 temperatureWater 94 98 99 99 98 94

[Method of Preparing Cellulose Fibers]

10 g of bleached kraft pulp was allowed to stand in 500 ml of waterovernight, thereby swelling the pulp, followed by adjusting thetemperature to 20° C. and adding 0.1 g of TEMPO and 1 g of sodiumbromide to provide a pulp suspension. While agitating, 10 mmols/g ofsodium hypochlorite per unit weight of the cellulose was added. On thisoccasion, about 1 N of a sodium hydroxide aqueous solution was added inorder to keep the pH of the pulp suspension at approximately 10.5,followed by reaction for 240 minutes and rinsing well with water toobtain pulp. The resulting pulp was adjusted to a solid concentration of1% with ion-exchanged water and agitated for about 60 minutes using ahigh-speed rotation mixer to obtain a dispersion of transparentcellulose fibers.

To the dispersion of the cellulose fibers were added an aqueous solution(which was obtained by weighing 5 g of PVA-124, manufactured by KURARECO., LTD. in a beaker, adding 500 g of pure water, and heating fordissolution to a temperature of 100° C. to provide a 1% solution) ofpolyvinyl alcohol serving as a water-soluble polymer, a water-solublepolyurethane (WD-725 of Mitsui Chemicals, Inc.), a chitosan aqueoussolution (made by Dainichiseika Color & Chemicals Mfg. Co., Ltd., andprepared by dissolving PVL in an acetic acid aqueous solution at a solidconcentration of 2%), and a starch aqueous solution (prepared bydispersing water-soluble starch in water at a solid concentration of 4%and heating at 90° C. for 1 hour). Kunipia and synthetic mica were,respectively, used as a layered inorganic compound after dilution withwater to make a solid concentration of 1%.

Examples 1-1-1-10 Preparation of Compositions for Film Formation inExamples 1-1-1-10

Different types of layered inorganic compounds and water solublepolymers were mixed and agitated with agitation blades using theformulation ratios and conditions of Table 1. The resulting dispersionswere each added to 100 parts of a dispersion of cellulose fibers at aratio indicated in Table 2 thereby preparing film-forming compositionsof Examples 1-1 to 1-10.

TABLE 2 Example Example Example Example Example Example 1-1 1-2 1-3 1-41-5 1-6 1% 62 50 40 48 60 54 transmittance (600 nm) Average 0.7 1.5 0.65 3.3 5.5 particle size after swelling Amount added 50 30 10 50 50 10 tocellulose dispersion (based on cellulose dispersion taken as 100)Average 0.7 1.5 0.6 5 3.3 5.5 particle size of composition for filmformation Oxygen 1.8 1.2 1.5 2 0.1 0.7 permeability at 30° C. and 70%Haze of 4.2 3.8 3.5 3.8 4.5 3.8 laminate Example Example Comp. Ex. Comp.Ex. Example Example 1-7 1-8 1-1 1-2 1-9 1-10 1% 52 62 81 82 68 72transmittance (600 nm) Average 8.5 12 0.5 3 1.2 4.2 particle size afterswelling Amount added 10 10 50 10 50 10 to cellulose dispersion (basedon cellulose dispersion taken as 100) Average 8.5 12 0.5 3 1.2 4.2particle size of composition for film formation Oxygen 1.4 2.1 5.2 4.82.8 3.5 permeability at 30° C. and 70% Haze of 3.5 4.8 5.4 5.1 4.2 3.9laminate

The coating dispersions prepared by use of the formulation ratios andthe dispersion preparation procedure indicated as formulations 1-1-1-10of Table 1 were each coated onto a 25 μm thick polyethyleneterephthalate film (Polyester film E5102, made by Toyobo Co., Ltd.)according to a bar coating method in a dry thickness of 1.0 μm and driedto form a barrier layer, thereby preparing barrier films.

[Preparation of a Barrier Film for Packaging Material in Example 1-1]

Further, in order to use the thus prepared barrier films as a packagingmaterial, a heat sealing layer was bonded to the barrier layer sidethrough an adhesive layer for lamination and aged at 50° C. for 4 daysto provide barrier films for use as a packaging material. Theheat-sealing layer used was 70 μm thick CPP (RXC22, made by MitsuiChemicals Tohcello, Inc.), and an adhesive used to form the adhesivelayer for lamination was an adhesive for two-component curablepolyurethane lamination (A525/A52 produced by Mitsui ChemicalsPolyurethanes, Inc.). The adhesive was coated onto the barrier layer bya gravure coating method so that the coating amount after drying was at4.0 g/m².

Example 2

Examples of the invention are more particularly described below, whichshould not be construed as limiting the invention thereto.

The respective materials of cellulose fibers, a water soluble polymer,and layered minerals indicated below were mixed at formulation ratiosindicated in the table thereby preparing coating dispersions.

[Method 1 of Preparing Cellulose Fibers]

10 g of bleached kraft pulp was allowed to stand in 500 ml of waterovernight to cause the pulp to be swollen, followed by adjusting thetemperature to 20° C. and further adding 0.1 g of TEMPO and 1 g ofsodium bromide thereby obtaining a pulp suspension. While agitating, 10mmols/g of sodium hypochlorite per unit weight of the cellulose wasadded. On this occasion, about 1 N of a sodium hydroxide aqueoussolution was added so that the pH of the pulp suspension was kept atabout 10.5. Thereafter, oxidation reaction was performed for 240minutes, followed by washing sufficiently with water to obtain a pulp.The thus obtained pulp was adjusted to a solid concentration of 1% withion-exchanged water and agitated for about 60 minutes using a high-speedrotation mixer, to obtain a dispersion of transparent cellulose fibers

[Method 2 of Preparing Cellulose Fibers]

The oxidized pulp obtained by the oxidation reaction in the above[method 1 of preparing cellulose fibers] was well washed with water andweighed so that the solid content was at 4 g. 50 g of a 4% dispersion ofKunipia F prepared according to [dispersion method 2 of layeredinorganic compound] described hereinlater, was added to the oxidizedpulp. Ion-exchanged water was further added thereto to make a solidcontent at 1%, followed by agitation for about 20 minutes by use of ahigh speed rotation mixer to obtain a dispersion containing cellulosefibers and Kunipia F.

[Preparation Method of Polyvinyl Alcohol]

5 g of commercially available PVA product (PVA-124, made by KURARE CO.,LTD.) was weighed in a beaker, to which 500 g of pure water was added.This was heated to 100° C. for dissolution to provide a 1% solution.

[Dispersion Method 1 of Layered Inorganic Compound]

Commercially available synthetic mica, PDM-5B (made by Topy Industries,Ltd.), was dispersed in water to make a 3% dispersion.

[Dispersion Method 2 of Layered Inorganic Compound]

Commercially available montmorillonite, Kunipia-F (made by KunimineIndustries Co., Ltd.), was dispersed in water to make a 4% dispersion.

[Method 1 of Preparing Coating Dispersion]

60 g of the 1% PVA solution was weighed in a beaker, to which 3.63 g ofa 3% dispersion of synthetic mica under agitation to prepare a mixeddispersion (1) of PVA/synthetic mica=50/10. Moreover, this dispersionwas heated and agitated at 80° C. The heating time under agitation was,respectively, set at 1 hour, 2 hours and 4 hours to provide mixeddispersions (2)-(4). While agitating 100 g of the dispersion of thecellulose nanofibers, 53 g of the mixed dispersions (1)-(4) were,respectively, added thereto to give cellulose/syntheticmica/PVA=100/10/50 and well agitated. The respective mixed dispersions(1)-(4) of cellulose, synthetic mica and PVA were provided as coatingdispersions (1)-(4). Further, the thus obtained coating dispersions wereheated and agitated at 80° C. for 1 hour to provide coating dispersions(5)-(8), respectively.

[Method 2 of Preparing Coating Dispersion]

100 g of a 1% dispersion of cellulose nanofibers was weighed in abeaker. After adequate agitation of the dispersion, 3.3 g of a 3%dispersion of synthetic mica was added under agitation. The resultingdispersion was provided as coating dispersion (9). Next, 50 g of a 1%PVA solution was added to the mixed dispersion to provide coatingdispersion (10). Further, this mixed dispersion was heated and agitatedat 80° C. for 1 hour to provide coating dispersion (11).

[Method 3 of Preparing Coating Dispersion]

100 g of a 1% dispersion of cellulose nanofibers was weighed in abeaker. This dispersion was well agitated, after which while agitatingthe dispersion, this was dispersed in coating solution (9), to which 3.3g of a 3% dispersion of synthetic mica had been added, by means of aultrasonic homogenizer for 30 seconds. The resulting mixed dispersionwas provided as coating dispersion (12).

[Method 4 of Preparing Coating Dispersion]

150 g of the dispersion obtained in the above [Method 2 of preparingcellulose fibers] was weighed in a beaker, to which 50 g of a 1% PVAsolution was added while agitating the dispersion. The resultingdispersion was provided as coating dispersion (13). This dispersion wasagitated at 80° C. for 1 hour under agitation to provide coatingdispersion (14). Moreover, the dispersion obtained in [method 2 ofpreparing cellulose fibers] was provided as coating dispersion (15).

Examples 2-1-2-12 Preparation of Gas Barrier Films in Examples 2-1-2-12

Gas barrier films were prepared such that coating dispersions (1)-(8),(10), (11), (13) and (14), which were prepared according to suchformulation ratios and preparation procedures as set out in theforegoing [Methods 1, 2 and 4 of preparing coating dispersions], wereeach coated onto a 25 μm thick polyethylene terephthalate film(polyester film E5102, made by TOYOBO CO., LTD.) by a bar coating methodin a dry thickness of 1.0 μm, followed by drying to form a gas barrierlayer.

[Preparation of Gas Barrier Films for Packaging Material in Examples 2-1to 2-12]

For use as a packaging material by coating the coating dispersions(1)-(8), (10), (11), (13) and (14) prepared before, a heat-sealing layerwas bonded to a gas barrier side through an adhesive layer forlamination according to a dry lamination method and aged at 50° C. for 4days to prepare a bas barrier film for packaging material. Theheat-sealing layer used was 70 μm thick CPP (RXC22, made by MitsuiChemicals Tohcello, Inc.), and the adhesive used to form the adhesivelayer for lamination was a two-component curable polyurethane adhesivefor lamination (A525/A52, made by Mitsui Chemicals Polyurethanes, Inc.).The adhesive was coated onto the gas barrier layer by a gravure coatingmethod in an amount of 3.0 g/m² after drying.

Comparative Examples 2-1-2-3

[Preparation of Gas Barrier Films in Comparative Examples 2-1-2-3]

Coating dispersions (9), (12) and (15), which were prepared according tosuch formulation ratios and preparation procedures as set out in theforegoing [Methods 3, 4 of preparing coating dispersions], were eachcoated onto a 25 μm thick polyethylene terephthalate film (polyesterfilm E5102, made by TOYOBO CO., LTD.) by a bar coating method in a drythickness of 1.0 μm, followed by drying to form a gas barrier layerthereby providing gas barrier films.

[Preparation of Gas Barrier Films for Packaging Material in ComparativeExamples 2-1 to 2-3]

For use as a packaging material by coating the coating dispersions (9),(12) and (15) prepared before, a heat-sealing layer was bonded to a gasbarrier side through an adhesive layer for lamination according to a drylamination method and aged at 50° C. for 4 days to prepare a bas barrierfilm for packaging material. The heat-sealing layer used was 70 μm thickCPP (RXC22, made by Mitsui Chemicals Tohcello, Inc.), and the adhesiveused to form the adhesive layer for lamination was a two-componentcurable polyurethane adhesive for lamination (A525/A52, made by MitsuiChemicals Polyurethanes, Inc.). The adhesive was coated onto the gasbarrier layer by a gravure coating method in an amount of 3.0 g/m² afterdrying.

The properties of the thus obtained gas barrier films were evaluated bythe following methods.

[Oxygen Permeability (Equal Pressure Method) (cm³/m²-day-Pa)]

Using an oxygen permeability measuring device MOCON (OX-TRAN2/21, madeby Modern Controls Inc), measurement was performed under conditions of30° C., 40% RH and 70% RH. The results of the measurement of oxygenpermeability of the gas barrier films are shown in Table 3.

[Measurement of Water Vapor Permeability]

The water vapor permeability (g/m²-day) was measured under conditions of40° C. and 90% RH using a water vapor permeability measuring devicePERMATRAN W-3/33MG (made by Modern Controls, Inc.). The results of themeasurement of water vapor permeability of the gas barrier films areshown in Table 3.

The laminate strength of each gas barrier film for packaging materialwas evaluated according to the following method.

[Measurement of Adhesion Strength]

The respective three-layered laminates were cut out into rectangulartest pieces having a width of 15 mm×a length of 10 cm. The test pieceswere each subjected to measurement of adhesion strength (N/15 mm)between the substrate and the PP film in accordance with the method ofJIS-K-7127 wherein T-shape peeling was effected at a tensile speed of300 mm/min. The results of the measurement of adhesion strength of thegas barrier film for packaging material are shown in Table 4. Further,the results of the measurement of oxygen permeability and water vaporpermeability are also shown in Table 4.

TABLE 3 EVALUATION RESUTS OF GAS BARRIER FILM Oxygen Water vaporPermeability permeability 30° C., 70% RH 40° C., 90% RH (cc/m²-day)(cc/m²-day) Example 2-1 1.0 13.9 Example 2-2 0.9 13.8 Example 2-3 0.913.9 Example 2-4 1.0 13.9 Example 2-5 0.9 14.0 Example 2-6 0.9 14.0Example 2-7 0.9 14.0 Example 2-8 1.0 14.1 Example 2-9 1.1 15.1 Example2-10 1.1 14.8 Example 2-11 3.1 15.1 Example 2-12 2.8 14.3 Comparative1.3 20.8 Example 2-1 Comparative 2.1 22.1 Example 2-2 Comparative 5.115.8 Example 2-3

TABLE 4 EVALUATION RESUTS OF GAS BARRIER FILM FOR PACKAGING MATERIALOxygen Water vapor Permeability permeability Adhesion 30° C., 70% RH 40°C., 90% RH strength (cc/m²-day) (cc/m²-day) (N/15 mm) Example 2-1 0.936.4 0.9 Example 2-2 0.84 6.4 0.9 Example 2-3 0.91 6.4 0.9 Example 2-40.95 6.3 0.9 Example 2-5 0.91 6.3 0.9 Example 2-6 0.87 6.3 0.9 Example2-7 0.94 6.4 0.9 Example 2-8 0.99 6.4 0.9 Example 2-9 1.05 6.4 0.6Example 2-10 1.03 6.4 0.6 Example 2-11 2.85 6.3 1.7 Example 2-12 2.726.4 1.7 Comparative 1.23 6.3 0.2 Example 2-1 Comparative 2.08 6.4 0.2Example 2-2 Comparative 4.87 6.4 1.3 Example 2-3

The comparison of Examples 2-1-2-10 using synthetic mica as the layeredinorganic compound with Comparative Examples 2-1, 2-2 and also ofExamples 2-11, 2-12 using montmorillonite with Comparative Example 2-3revealed that the addition of PVA enhanced the dispersibility of thelayered inorganic compound and contributed to expanding thelayer-to-layer gap of the layered inorganic compound thereby improvingbarrier properties. Further, the addition of PVA could fill the gapsamong the cellulose nanofibers, layered inorganic compound and basematerial thereby improving adhesion.

In view of Examples 2-2-2-4 and 2-6-2-8 wherein the heating andagitating time was changed, it was found that if the time was elongated,the layered inorganic compound became too small in size, with thetendency that barrier properties lowered slightly.

Furthermore, the comparison between Examples 2-1-2-10 using syntheticmica as the layered inorganic compound and Comparative Example 2-2revealed that the layered inorganic compound was broken down bytreatment with a homogenizer, so that barrier properties loweredconsiderably.

The comparison of Examples 2-1, 2-2 with Examples 2-9, 2-10 demonstratedthat because the layered inorganic compound had higher affinity for PVAthan for cellulose nanofibers, the addition of cellulose nanofibersafter preliminary mixing of PVA and layered inorganic compound leads tobetter dispersability, resulting in better barrier properties.

EXPLANATION OF REFERENCE NUMERALS

-   -   1 . . . Base material    -   2 . . . Gas barrier layer    -   4 . . . Adhesive layer for lamination    -   6 . . . Heat sealing layer

The invention claimed is:
 1. A method for preparing a cellulosedispersion, comprising: providing cellulose; preparing cellulosenanofibers by defibrating the cellulose; and adding a water-solublepolymer and a swollen layered inorganic compound to a dispersioncontaining the cellulose nanofibers, the adding the water-solublepolymer and swollen layered inorganic compound comprising: mixing thewater-soluble polymer and the swollen layered inorganic compound toprepare a dispersion of the water-soluble polymer and the swollenlayered inorganic compound; and mixing the dispersion of thewater-soluble polymer and the swollen layered inorganic compound withthe dispersion containing the cellulose nanofibers, so that thecellulose nanofibers and the water-soluble polymer are intercalatedbetween layers of the swollen layered inorganic compound.
 2. The methodfor preparing a cellulose dispersion as defined in claim 1, wherein theadding the swollen water-soluble polymer and layered inorganic compoundfurther comprises: agitating the dispersion of the mixture of thewater-soluble polymer and the swollen layered inorganic compound, sothat the agitated dispersion of the water-soluble polymer and theswollen layered inorganic compound is mixed with the dispersioncontaining the cellulose nanofibers.
 3. The method for preparing acellulose dispersion as defined in claim 1, wherein the adding thewater-soluble polymer and swollen layered inorganic compound furthercomprises: heating the dispersion of the water-soluble polymer and theswollen layered inorganic compound, so that the heated dispersion of thewater-soluble polymer and the swollen layered inorganic compound ismixed with the dispersion containing the cellulose nanofibers.
 4. Themethod for preparing a cellulose dispersion as defined in claim 1,wherein the adding the water-soluble polymer and layered inorganiccompound further comprises: heating the mixture of the dispersion of thewater-soluble polymer and the swollen layered inorganic compound and thedispersion containing the cellulose nanofibers.
 5. The method forpreparing a cellulose dispersion as defined in claim 1, wherein theadding the water-soluble polymer and swollen layered inorganic compoundfurther comprises: after an aqueous solution of the water-solublepolymer and the swollen inorganic compound have been mixed and agitated,heating the solution of the water-soluble polymer and the swolleninorganic compound.
 6. The method for preparing a cellulose dispersionas defined in claim 1, wherein the cellulose nanofibers and thewater-soluble polymer are intercalated between the layers of the swollenlayered inorganic compound while the swollen layered inorganic compoundis dispersed.
 7. The method for preparing a cellulose dispersion asdefined in claim 1, wherein individual gaps between the layers of theswollen layered inorganic compound are not less than 14 angstroms.